To survive within the hostile environment of the infected host, pathogenic microorganisms must be able to sense and adapt to changing environmental conditions. This adaptation requires the coordinated regulation of multiple cellular factors. Like many infectious agents, the human fungal pathogen Cryptococcus neoformans uses the conserved signaling molecule cyclic AMP (cAMP) to regulate its response to external stresses. The central components of cAMP signal transduction pathways are highly conserved among microorganisms. However, the main hypothesis of this proposal is that the upstream activating signals and the downstream effectors of cAMP are functionally specialized in microbial pathogens. This specialization allows pathogenic organisms to use cAMP signaling to specifically control their virulence potential. Over the past several years, we have demonstrated that the C. neoformans cAMP pathway is required for adaptation to the host environment. This pathway regulates the induction of capsule and melanin, two cellular factors required for pathogenesis. This regulation occurs primarily at the level of transcription. Therefore, we designed the experiments of this proposal to identify trans- and cis-acting regulatory elements that control the transcription of capsule-associated genes. Specific Aim 1 proposes bioinformatic and transcriptional profiling approaches to identify transcription factors that control C. neoformans capsule gene expression. Specific Aim 2 outlines detailed testing of selected transcriptional regulators to define their role in capsule induction. Experiments in Specific Aim 3 will define the direct and indirect target genes of the transcription factors identified in the first two Aims. Upon completion, these experiments will offer new insight into the ways in which this specific pathogen senses and responds to its host. By defining new functions for conserved signaling pathways, these experiments will also explore broader issues in environmental sensing, cellular stress, and microbial virulence. PUBLIC HEALTH RELEVANCE: In order to better treat infectious diseases, we must understand the ways in which infectious microorganisms survive within their host. The experiments in this proposal will study Cryptococcus neoformans, an important opportunistic fungal pathogen in AIDS patients, to define the cellular factors required for formation of a protective surface capsule. Capsule production will also be used as a model to better understand more fundamental issues of the interaction between microorganisms and the infected host.